The present invention relates generally to the recovery of subterranean deposits, and more particularly to a method and system for accessing subterranean deposits from the surface.
Subterranean deposits of coal typically contain substantial quantities of entrained methane gas. There are many uses for methane gas extracted from subterranean deposits. Substantial obstacles, however, have frustrated more extensive development and use of methane gas deposits in coal seams. A common problem in producing methane gas from coal seams may be vertical separation of multiple thin layers of coal within a coal seam. Although coal seams may extend over large areas of up to several thousand acres, the depth of the multiple layers in the coal seam may vary from very shallow to very deep. Vertical wells drilled into the coal deposits for obtaining methane gas can only drain a fairly small radius of methane gas around the vertical well. Further, coal deposits are not amenable to pressure fracturing and other methods often used for increasing gas production from conventional rock formations. As a result, production of gas may be limited in volume. Additionally, coal seams are often associated with subterranean water, which must be drained from the coal seam in order to produce the methane.
The present invention provides an improved method and system for accessing subterranean deposits from the surface that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, the present invention provides an articulated well with a drainage pattern that provides access to a large subterranean area from the surface.
In accordance with one embodiment of the present invention, a subterranean drainage pattern for accessing a subterranean zone includes at least one undulating well bore. The undulating well bore includes at least one inclining portion drilled through the subterranean zone at an inclination sloping toward an upper boundary of the single layer of subterranean deposits and at least one declining portion drilled through the subterranean zone at a declination sloping toward a lower boundary of the single layer of subterranean deposits. At least one bending portion couples the at least one inclining portion and the at least one declining portion to form a waveform.
Embodiments of the present invention may have some, all, or none of the following technical advantages. In particular embodiments, an improved drainage pattern may include undulating well bores that provide access to multiple regions of the subterranean zone. For example, a pinnate drilling pattern may include a main well bore and multiple opposed lateral well bores. The main well bore, the opposed lateral well bores, or both may include undulating well bores to maximize access to a subterranean zone from a single vertical well bore. In one embodiment, undulating well bores may provide access to minerals and gas contained in a very thick layer of subterranean deposits. In another embodiment, undulating well bores may provide access to multiple layers of subterranean deposits separated by layers of impermeable or substantially impermeable material. The length of undulating well bore may be increased to maximize the area horizontally covered by the undulating well bore. Similarly, the height of the undulating well bore may be increased to maximize the area vertically covered by the undulating well bores.